Oxidation-Resistant Coated Superalloy

ABSTRACT

A coating-substrate combination includes: a Ni-based superalloy substrate comprising, by weight percent: 2.0-5.1 Cr; 0.9-3.3 Mo; 3.9-9.8 W; 2.2-6.8 Ta; 5.4-6.5 Al; 1.8-12.8 Co; 2.8-5.8 Re; 2.8-7.2 Ru; and a coating comprising, exclusive of Pt group elements, by weight percent: Ni as a largest content; 5.8-9.3 Al; 4.4-25 Cr; 3.0-13.5 Co; up to 6.0 Ta, if any; up to 6.2 W, if any; up to 2.4 Mo, if any; 0.3-0.6 Hf; 0.1-0.4 Si; up to 0.6 Y, if any; up to 0.4 Zr, if any; up to 1.0 Re, if any.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 16/177,974,filed Nov. 1, 2018, entitled “Oxidation-Resistant Coated Superalloy”which is a divisional of U.S. patent application Ser. No. 13/969,689,filed Aug. 19, 2013, entitled “Oxidation-Resistant Coated Superalloy”,now abandoned, which claims benefit of U.S. Patent Application No.61/691223, filed Aug. 20, 2012, U.S. Patent Application No. 61/720155,filed Oct. 30, 2012, and U.S. Patent Application No. 61/785596, filedMar. 14, 2013, all entitled “Oxidation-Resistant Coated Superalloy”, thedisclosures of which five applications are incorporated by reference intheir entireties herein as if set forth at length.

BACKGROUND

The disclosure relates to high temperature nickel-based superalloys.More particularly, the disclosure relates to oxidation resistantsuperalloy coatings for such superalloys.

A long-developed field has existed in turbine engine turbine blademetallurgy. Cast single-crystal nickel-based superalloys are used forturbine section blades in gas turbine engines. Such alloys arenotoriously subject to oxidation and require oxidation-resistantcoatings. However, many coatings exhibit excessive secondary reactionzone (SRZ) formation with the substrate material.

Prior blade substrate and coating combinations that have been proposedinclude those in US Pub. Nos. 2006/0093851 A1, 2009/0075115 A1, and2009/0274928 A1. Metallic coatings may be the outermost layer (subjectto oxidation layers, etc.) or may be bond coats for ceramic thermalbarrier coatings (TBC) deposited thereatop.

SUMMARY

One aspect of the disclosure involves a coating-substrate combinationinvolving a Ni-based superalloy substrate comprising, by weight percent:2.0-5.1 Cr; 0.9-3.3 Mo; 3.9-9.8 W; 2.2-6.8 Ta; 5.4-6.5 Al; 1.8-12.8 Co;2.8-5.8 Re; 2.8-7.2 Ru; and a coating comprising, exclusive of Pt groupelements, by weight percent: Ni as a largest content; 5.8-9.3 Al; 4.4-25Cr; 3.0-13.5 Co; up to 6.0 Ta, if any; up to 6.2 W, if any; up to 2.4Mo, if any; 0.3-0.6 Hf; 0.1-0.4 Si; up to 0.6 Y, if any; up to 0.4 Zr,if any; up to 1.0 Re, if any.

One aspect of the disclosure involves a coating-substrate combinationinvolving a Ni-based superalloy substrate comprising, by weight percent:2.0-6.0 Cr; 0.5-4.0 Mo; 3.0-10-0 W; 2.0-7.0 Ta; 5.0-7.0 Al; 1.0-14.0 Co;2.0-6.0 Re; 1.0-8.0 Ru; and a coating comprising, exclusive of Pt groupelements, by weight percent: Ni as a largest content; 5.0-11.0 Al;3.0-25 Cr; 3.0-17.0 Co; up to 7.0 Ta, if any; up to 6.2 W, if any; up to3.0 Mo, if any; 0.05-0.7 Hf; 0.1-0.4 Si; up to 0.7 Y, if any; up to 0.7Zr, if any; up to 1.0 Re, if any.

In additional or alternative embodiments of any of the foregoingembodiments, the coating comprises exclusive of Pt group elements, byweight percent: 0.4-0.6 said Hf; 0.2-0.4 said Si.

In additional or alternative embodiments of any of the foregoingembodiments, the coating has less than 1.0 weight percent overall saidPt group elements combined.

In additional or alternative embodiments of any of the foregoingembodiments, in weight percent exclusive of Pt group elements, thecoating has less than 1.0 weight percent individually other elements.

In additional or alternative embodiments of any of the foregoingembodiments, the substrate falls within one of the broader ranges ofTable VI; and the coating falls within the associated broader range ofTable VI.

In additional or alternative embodiments of any of the foregoingembodiments, the coating and substrate fall within the narrowerassociated ranges.

In additional or alternative embodiments of any of the foregoingembodiments, the coating has said weight percent combined of said Y, Hf,Zr, and Si of 0.5-1.5 weight percent.

In additional or alternative embodiments of any of the foregoingembodiments, the coating has 3.0-5.8 said weight percent Ta; and thecoating has combined contents, if any, of no more than 6.5% by weightRu, said Ta, and said Re.

In additional or alternative embodiments of any of the foregoingembodiments, the coating has less than 0.50 weight percent Ru, if any.

In additional or alternative embodiments of any of the foregoingembodiments, the coating has less than 0.50 or 0.10 said weight percentRe, if any.

In additional or alternative embodiments of any of the foregoingembodiments, a ratio of said substrate weight percent Re to said coatingweight percent Re, if any, is in excess of 10.0.

In additional or alternative embodiments of any of the foregoingembodiments, a SRZ, if any, is less than 0.001 inch (0.025 mm) thick.

In additional or alternative embodiments of any of the foregoingembodiments, the article/substrate may be a single crystal alloy such asa turbine blade.

In additional or alternative embodiments of any of the foregoingembodiments, the substrate has a density of 0.315-0.327 pounds per cubicinch (8.72-9.05 g/cm³).

Another aspect of the disclosure involves an article comprising: aNi-based superalloy substrate comprising, by weight percent: 4.0-6.0 Cr;1.0-2.0 Mo; 5.0-6.0 W; 5.0-6.0 Ta; 5.0-6.0 Al; 5.0-7.0 Co; 5.0-6.0 Re;2.0-3.0 Ru; and a coating comprising, exclusive of Pt group elements, byweight percent: Ni as a largest content; 5-11 Al; 3-15 Cr; 9-16 Co; upto 7 Ta, if any; up to 6 W, if any; up to 3 Mo, if any; 0.05-0.7 Hf;0.1-0.5 Si; up to 0.7 Y, if any; up to 0.7 Zr, if any; up to 1.0 Re, ifany.

Another aspect of the disclosure involves an article comprising: aNi-based superalloy substrate comprising, by weight percent: 2.0-3.0 Cr;2.0-4.0 Mo; 8.0-10.0 W; 2.0-3.0 Ta; 6.0-7.0 Al; 6.0-8.0 Co; 4.0-5.0 Re;6.0-8.0 Ru; and a coating comprising, exclusive of Pt group elements, byweight percent: Ni as a largest content; 5-11 Al; 3-15 Cr; 9-17 Co; upto 7 Ta, if any; up to 6 W, if any; up to 3 Mo, if any; 0.05-0.7 Hf;0.1-0.5 Si; up to 0.7 Y, if any; up to 0.7 Zr, if any; up to 1.0 Re, ifany.

Another aspect of the disclosure involves an article comprising: aNi-based superalloy substrate comprising, by weight percent: 2.0-3.0 Cr;1.0-3.0 Mo; 3.0-5.0 W; 3.0-4.0 Ta; 5.0-7.0 Al; 1.0-3.0 Co; 2.0-4.0 Re;4.0-6.0 Ru; and a coating comprising, exclusive of Pt group elements, byweight percent: Ni as a largest content; 5-11 Al; 3-15 Cr; 9-16 Co; upto 7 Ta, if any; up to 6 W, if any; up to 3 Mo, if any; 0.05-0.7 Hf;0.1-0.5 Si; up to 0.7 Y, if any; up to 0.7 Zr, if any; up to 1.0 Re, ifany.

Another aspect of the disclosure involves an article comprising: aNi-based superalloy substrate comprising, by weight percent: 2.0-3.0 Cr;2.0-3.0 Mo; 7.0-9.0 W; 2.0-4.0 Ta; 5.0-6.0 Al; 7.0-9.0 Co; 3.0-5.0 Re;4.0-6.0 Ru; and a coating comprising, exclusive of Pt group elements, byweight percent: Ni as a largest content; 5-11 Al; 3-15 Cr; 9-17 Co; upto 7 Ta, if any; up to 6 W, if any; up to 3 Mo, if any; 0.05-0.7 Hf;0.1-0.5 Si; up to 0.7 Y, if any; up to 0.7 Zr, if any; up to 1.0 Re, ifany.

Another aspect of the disclosure involves an article comprising: aNi-based superalloy substrate comprising, by weight percent: 3.0-4.0 Cr;0.5-2.0 Mo; 6.0-8.0 W; 4.0-5.0 Ta; 5.0-7.0 Al; 1.0-3.0 Co; 4.0-5.0 Re;3.0-5.0 Ru; and a coating comprising, exclusive of Pt group elements, byweight percent: Ni as a largest content; 5-11 Al; 3-15 Cr; 9-17 Co; upto 7 Ta, if any; up to 6 W, if any; up to 3 Mo, if any; 0.05-0.7 Hf;0.1-0.5 Si; up to 0.7 Y, if any; up to 0.7 Zr, if any; up to 1.0 Re, ifany.

Other aspects involve methods for using the article comprising: heatingthe article to a temperature of at least 2000 F (1093 C) for at least400 hours while an SRZ, if any, remains less than 0.002 inch (0.05 mm)thick.

Other aspects involve methods for forming the article.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pair of sectional photomicrographs of a first superalloysubstrate/superalloy coating combination in an as-applied condition(left) and a post-exposure condition (right).

FIG. 2 (Table I) is a table of nominal (intended) substratecompositions.

FIG. 3 (Table II) shows nominal (intended) coating compositions.

FIG. 4 (Table III) is a table of measured substrate compositions.

FIG. 5 (Table IV) is a table of measured coating compositions.

FIGS. 6A and 6B in serial combination (collectively FIG. 6) (Table V)are a table of predicted and observed SRZ formation.

FIGS. 7-12 are respective sectional photomicrographs of second throughseventh superalloy substrate/superalloy coating combinations in apost-exposure condition.

FIGS. 13A-13D in serial combination (collectively FIG. 13) (Table VI)are a table of elemental tolerances for specifications of hypothesizedindividual substrates for substrate-coating pairs.

FIGS. 14A and 14B in serial combination (collectively FIG. 14) (TableVII) are a table of elemental tolerances for specifications ofhypothesized individual coatings for substrate-coating pairs.

FIGS. 15A-15D in serial combination (collectively FIG. 15) (Table VIII)are a table of elemental tolerances for coatings for hypothesizedsubstrate-coating pairs.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1 shows an article 20 comprising a Ni-based single crystalsubstrate 22 with a Ni-based coating 24 thereatop. In this example, thesubstrate is TMS-162 and the coating is MDC-150L (Alcoa HowmetThermatech Coatings, Whitehall, Mich., US). An epoxy mount for thesectioning is shown as 26. The coating 24 is applied directly to theexposed surface of substrate (e.g., via a physical vapor deposition(PVD) process such as cathodic arc deposition). With an exemplaryattempt at an oxide-resistant superalloy coating (e.g., FIG. 1, althoughnot necessarily prior art) one sees the substrate 22 and the coating 24.

The coating 24 is further divided into regions including an additivezone 27 and a diffusion zone 28 below the additive zone (representingsubstrate material into which additive coating material has diffused).Exemplary as-applied thickness is 0.002-0.004 inch (0.05-0.10 mm), morebroadly, 0.001-0.006 inch (0.025-0.15 mm). An oxide layer at the coatingsurface may be just perceptible.

A highly columnar secondary reaction zone (SRZ) 32 has a thickness whichmay exceed 0.001 inch (0.025 mm). The SRZ is widely accepted as being abrittle P-phase that causes unacceptable reductions in mechanicalproperties such as fatigue and creep (See, e.g., W. S. WALSTON et al.,“A New Type of Microstructural Instability in Superalloys-SRZ”,Superalloys 1996, published Sep. 1, 1996, pages 9-18, The Minerals,Metals & Materials Society, Warrendale, Pennsylvania and O. LAVIGNE etal., “Relationships Between Microstructural Instabilities and MechanicalBehaviour in New Generation Nickel-Based Single Crystal Superalloys”,Superalloys 2004, published Jan. 1, 2006, pages 667-675, The Minerals,Metals & Materials Society, Warrendale, Pa.).

The exemplary post-exposure micrographs in FIG. 1 and further figuresbelow reflect heating in air at ambient pressure to a temperature of2000 F (1093 C) for a period of 400 hours. The SRZ 32′ has expanded to athickness in excess of 0.005 inch (0.13 mm). The expanded SRZ 32′ moregreatly compromises strength properties.

Table I (FIG. 2) shows nominal (intended) substrate compositions. Theserepresent a select group of high-Re, high creep-resistance materials.Table II (FIG. 3) shows nominal (intended) coating compositions. Theseand particular combinations thereof were selected based upon ananalytical model to predict the formation of SRZ. In an initialexperimental calibration step, EPMA elemental composition depth profilesare performed on selected actual coating/alloy couples both in theas-coated and post-exposure conditions to calibrate the diffusion model.Alloy/coating couples are selected to provide a wide range of degrees ofSRZ formation. In a simulation calibration step, Thermo-Calc™ andDICTRA™ software (both of Thermo-Calc Software, Stockholm, Sweden),using both thermodynamic and mobility databases, are used to determinethe evolution of the different phase fractions with depth, from thesurface of the coating, through the inter-diffusion zone and to wellinside the substrate. Experimental depth profiles from Phase 1 are usedto calibrate the databases to match more closely actual interactionbetween the types coating and alloys at stake. In an experimentalvalidation step, more experimental coating/alloy couples are evaluatedfor their level of SRZ formation, but with no depth profile: onlyaverage actual composition of both coating and alloy are used to linkthe couple to the SRZ formation metric. In a simulation validation step,blind simulations are performed to validate the performance of thecalibrated software on coating/alloy couples with known level of SRZformation by the experimental team, but unknown to the simulation team.Thereafter, a statistical analysis includes formulating a statisticalmodel followed by supplementary diffusion simulations aimed at producingoptimized input for the multiple regression model. This is used todefine possible preferred alloy and coating combinations. Thereafter,these preferred alloy and coating combinations are ultimately used forvalidation of the regression model predictions with SRZ evaluation pre-and post-exposure. The observance of SRZ and/or measurement of othermechanical properties may be used to determine satisfactorycombinations.

Because the manufacture process is subject to some uncertainty, theactual compositions differed from the intended compositions. Tables III(FIG. 4) and IV (FIG. 5), respectively are measured substrate andcoating compositions. Hf was measured for only two. Hf in the substratehelps increase oxidation resistance. Exemplary Hf content is about 0.15weight percent (which may be a nominal target content), more broadly,0.10-0.20, or more broadly 0.1-0.2.

The Table IV coating composition was determined on the coating itselfwith microprobe analysis, as-coated, before exposure. It is noted thatcoating composition will differ from ingot composition due todifferential proportions of different elements in the ingot depositingon the substrate. These relative deposition efficiencies depend onfactors including the particular materials, deposition apparatus,operating parameters and the like. Based upon know effects of suchfactors, an ingot composition can be determined for a desired coatingcomposition, subject to some error and possible trial and erroradjustment. For a typical blade, coating composition will reflect thepre-exposure values until the blade is used (unless a pre-use exposureis applied to the blade). For the foregoing reasons, as-applied coatingmeasurements are used rather than ingot or post-exposurevalues/measurements.

Table V (FIG. 6) shows numbers the model generated as predictive of thepresence of SRZ as well as a characterization of observed extent of SRZformation of the coatings of Table IV on the substrates of Table III,after exposure.

FIGS. 7-10 each show as-applied and post-exposure conditions of severalof the Table V combinations. As is noted above, these combinations mayrepresent the final article (e.g., a cast single-crystal nickel-basedsuperalloy blade) or there may be additional coating layers such as aceramic thermal barrier coating (TBC) deposited thereatop. Exemplary TBCincludes a ceramic layer made of partially-stabilized zirconia or aceramic layer that has a thermal conductivity of less than zirconiastabilized by about seven weight percent yttria (7YSZ). In yet anothervariation, a platinum group metal may be applied (e.g., plated) to thesubstrate prior to coating application. After any heat treatment or use,diffusion of the one or more platinum group elements into the coatingapplied thereatop may leave the resultant coating with up to 60% (byweight) of said at least one platinum group metal to further enhanceoxidation resistance of the coating. The remaining non-platinum groupelements would remain substantially in the same proportions as in thetables. Platinum group metals will diffuse into the coating at muchlower temperatures than the exposure/use temperatures. In a furthervariation, such platinum may be applied after the coating is applied andthen diffused into the coating (thereafter, a ceramic coating, if any,may be applied).

From FIGS. 6-10, it is clear that we have demonstrated at least the coreof a space of coating-substrate combinations having advantageousproperties of lack of SRZ formation in creep-resistant SX alloys.

FIG. 11 shows one of the borderline SRZ formation entries from Table V.It is characterized as borderline because of the multi-phase, columnarnature of at least part of the alloy-coating interdiffusion zone, butnot as clearly discernable as what was observed on FIG. 1 or FIG. 12 inthe post-exposure condition. This manifests itself as a greater visibledifference between the additive zone and the diffusion zone.

FIG. 12 shows one of the observed SRZ formation combinations. Themorphology of the SRZ, however, apparently differs from FIG. 1.

In contrast, US 2009/0274928 A1 appears to largely involve relativelylow-Cr and high-Re coating contents which may be conceding oxidationresistance to provide compatibility between coating and substrate. Theforegoing examples, however, now demonstrate an alternative to suchtradeoff. Rhenium and ruthenium in a coating are expensive and lossesduring deposition are inevitable. Losses may be particularly significantwith thermal spray techniques (which were probably used inUS2008/0274928 because of the presence of Amdry™ 9954 (Sulzer Metco,Inc., Westbury, N.Y.), a powder used for thermal spray). Having no orlow Re and Ru provides a lower cost coating.

US2009/0075115 A1 identifies a transition metal layer between substrateand bond coat to prevent reaction. U.S. Pat. Nos. 6,306,524, 6,720,088,and 6,921,586 disclose a Ru-containing diffusion barrier at theinterface to locally reduce the mobility of elements known to increasethe probability of SRZ formation. Similarly, U.S. Pat. No. 6,746,782proposes a combination of chromium, rhenium, tungsten, or ruthenium toact as a diffusion barrier. The foregoing examples, however, nowdemonstrate an alternative to such requirement. The present examples areselected to provide both thermodynamic and diffusion kinetics betweenthe alloys and the coatings that prevent formation of deleterious SRZphase.

US 2006/0093851 A1 adopted a nickel aluminide coating with relativelylow content in chromium. The coatings in present FIG. 3 mostly havehigher content in chromium, which is known to be beneficial to bothoxidation and hot corrosion resistance, while also being resistant toSRZ formation when deposited on most of the proposed alloys.

One characterization of the coating-substrate space involves a Ni-basedsuperalloy substrate comprising, by weight percent: 2.0-5.1 Cr; 0.9-3.3Mo; 3.9-9.8 W; 2.2-6.8 Ta; 5.4-6.5 Al; 1.8-12.8 Co; 2.8-5.8 Re; 2.8-7.2Ru; and a coating comprising, exclusive of Pt group elements, by weightpercent: Ni as a largest content; 5.8-9.3 Al; 4.4-25 Cr; 3.0-13.5 Co; upto 6.0 Ta, if any; up to 6.2 W, if any; up to 2.4 Mo, if any; 0.3-0.6Hf; 0.1-0.4 Si; up to 0.6 Y, if any; up to 0.4 Zr, if any; up to 1.0 Re,if any. Although Table III does show some examples in this space ashaving SRZ formation, that only confirms the otherwise unexpected natureof the benefits of the space as a whole.

Furthermore, exemplary coating combined content of the reactive elementsY, Hf, Zr, and Si is 0.5-2.0 weight percent, more particularly, it maybe 0.5-1.5 weight percent or 0.5-1.0 weight percent. Reactive elementranges serve (individually and combined) to provide enough oxidationresistance (reason for min. value) without forming deleterious phasesfor oxidation if there is too much (reason for max. value). Also,modeling indicates a particular combined tantalum and tungsten contentto tailor the coating physical properties to the alloy's, whilecontrolling the SRZ formation and maximize oxidation resistance of thecoating. The model indicates a binary situation in weight percent whereeither 6.0≤W+Ta≤13.0 or Ta+W≤0.05. The model also indicates furthercharacterizations of chromium and nickel weight percent content where55.0≤Ni+Cr≤67.0 and Ni≤52 in the coating and Cr weight percent in thecoating is at least the same as Cr weight percent in the substrate. Anyof the FIG. 13/14 or FIG. 15 combinations discussed below may further bemodified by one-to-all or any combination of these relationships. Again,if platinum group elements are present, the relationships would applyexcluding such elements as noted above.

Exemplary substrate density is of 0.310-0.328 pounds per cubic inch(8.58-9.08 g/cm³), more particularly, 0.315-0.327 pounds per cubic inch(8.72-9.05 g/cm³). Exemplary substrate creep resistance (which, however,might not be achieved by some of the tested alloys) is at least 50 F (28C) greater than that of PWA1484 (balance Ni plus impurities and weightpercent: 5 Cr; 10 Co; 1.9 Mo; 5.9 W; 8.7 Ta; 5.65 Al; 0.1 Hf; 3 Re, 8.95g/cm³). At least 50 F (28 C) over PWA 1484 means that whatever therupture life of PWA 1484 at a given temperature and stress, the subjectalloy would have the same life at the same stress and at least a 50 F(28 C) higher temperature. In practice, at the 1800 F/45 ksi (982° C. &310 MPa) test condition, the 50 F (28 C) improvement would likely beassociated with at least 234 hour rupture life (using an estimated 75.0hour compromise of the 85.0 hour and 59.4 hour figures in Table IX).Table IX also shows data for CMSX-4® alloy of Cannon-MuskegonCorporation, Muskegon, Mich. ((balance Ni plus impurities and weightpercent: 6.5 Cr; 9 Co; 0.6 Mo; 6 W; 6.5 Ta; 5.6 Al; 0.1 Hf; 3 Re, 8.70g/cm³).

Returning to Table III of FIG. 4, it is seen that CPW-V1, has a muchlower density than PWA 1484; CPW-V2, 6, 9, and 10 have a moderatelylower density; and CPW-V3, 4, 7, 8, and 11 have slightly lower toslightly higher density. From the partial date in Table IX, it is seenthat there is a tradeoff in density and strength. With density muchlower than PWA 1484 ((e.g., 0.313-0.318 pounds per cubic inch (8.66-8.80g/cm³)), one might accept up to a 25 F (14 C) reduction in creepcapability. With density moderately lower than PWA 1484 ((e.g.,0.319-0.321 pounds per cubic inch (8.83-8.89 g/cm³)), up to a 25 F (14C) increase in creep capability would present a clear advantage over PWA1484. With density slightly lower to slightly higher than PWA 1484((e.g., 0.322-0.326 pounds per cubic inch (8.91-9.02 g/cm³)), greaterthan 30 F (17 C), more particularly greater than 40 F (22 C) or greaterthan 50 F (28 C), increase in creep capability would also present aclear advantage over PWA 1484.

TABLE IX Alloy Rupture Life under Test Conditions Rupture Life (Hours)1800° F. & 45ksi 2000° F. & 20ksi Alloy (982° C. & 310MPa) (982° C. &138MPa) PWA 1484* 85.0 220 PWA 1484 59.4 151 CMSX-4 ®** 74.0 129 CPW-V151.1 36.8 CPW-V2 127 566 CPW-V3 169 700 CPW-V4 189 166 CPW-V5 157 174CPW-V6 147 176 CPW-V7 127 70 CPW-V8 152 280 CPW-V9 121 351 CPW-V10 155132 CPW-V11 159 307 Min. 1 40 30 Min. 2 80 200 Min. 3 100 400 Min. 4 120500 Min. 5 150 600 *Historical data from a different testing house thanthe remaining data. **Trademark of Cannon-Muskegon Corporation,Muskegon, Michigan.

Exemplary Min. values are given associated with various levels ofperformance relative to PWA 1484. Rather than using hours, alternativeMin. values may be expressed relative to the PWA 1484 figures as apercentage (or fractional) increase or decrease at either or both of thetwo measurement conditions given.

If individual specifications are made for the substrate, coating, orsubstrate coating pairs, exemplary tolerances around the substrates andcoatings for the particular SRZ-free examples are shown in Tables VI andVII of FIGS. 13 and 14. Levels of other elements (whether Pt group orimpurities) may be at exemplary levels mentioned above and in theclaims.

Further combinations are seen in Table VIII of FIG. 15 whereinindividual of the named substrates and several groups of the namedsubstrates are respectively characterized by two levels of compositionbreadth. Based upon modeling, coating composition range for beneficiallack of SRZ formation is given as are two levels of composition breadthassociated with a combination of such lack of SRZ formation andoxidation resistance. The nominal “0” maximum values may be regarded asincluding up to impurity levels but would typically be less than 0.1 or0.05. Any of the four range combinations for a given substrate-coatingcombination may be used as an alternative characterization.

Where a measure is given in English units followed by a parentheticalcontaining SI or other units, the parenthetical's units are a conversionand should not imply a degree of precision not found in the Englishunits.

One or more embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made. For example, whenimplemented as a replacement for a baseline substrate/coating system ina given application, details of the baseline and application mayinfluence details of any particular implementation. Accordingly, otherembodiments are within the scope of the following claims.

What is claimed is:
 1. An article comprising: a Ni-based superalloysubstrate comprising, by weight percent: 2.0-5.1 Cr; 0.9-3.3 Mo; 3.9-9.8W; 2.2-6.8 Ta; 5.4-6.5 Al; 1.8-12.8 Co; 2.8-5.8 Re; 2.8-7.2 Ru; and acoating comprising, exclusive of Pt group elements, by weight percent:Ni as a largest content; 5.8-9.3 Al; 4.4-25 Cr;
 3. 0-13.5 Co; up to 6.0Ta, if any; up to 6.2 W, if any; up to 2.4 Mo, if any; 0.3-0.6 Hf;0.1-0.4 Si; up to 0.6 Y, if any; up to 0.4 Zr, if any; up to 1.0 Re, ifany.
 2. The article of claim 1 wherein: the substrate comprises 0.05-0.7weight percent Hf.
 3. The article of claim 1 wherein: the substrate hasa 1800° F. & 45 ksi (982° C. & 310 MPa) rupture life of at least 120hours.
 4. The article of claim 1 wherein: the coating comprisesexclusive of Pt group elements, by weight percent: 0.4-0.6 said Hf;0.2-0.4 said Si.
 5. The article of claim 4 wherein: the coating has lessthan 1.0 weight percent overall said Pt group elements combined.
 6. Thearticle of claim 1 wherein: in weight percent exclusive of Pt groupelements, the coating has less than 1.0 weight percent individuallyelements other than said Ni, Al, Cr, Co, Ta, W, Mo, Hf, Si, Y, Zr, Re,and Pt group elements, if any.
 7. The article of claim 1 wherein: thesubstrate also falls within one of the broader ranges of Table VI; andthe coating also falls within the associated broader range of Table VII.8. The article of claim 7 wherein: the coating and substrate fall withinthe narrower associated ranges.
 9. The article of claim 1 wherein: inweight percent the coating has 6.0≤W+Ta≤13.0 or Ta+W≤0.05.
 10. Thearticle of claim 1 wherein: in weight percent the coating has55.0≤Ni+Cr≤67.0 and Ni≤52; and Cr weight percent in the coating is atleast the same as Cr weight percent in the substrate.
 11. The article ofclaim 1 wherein: the coating has said weight percent combined of said Y,Hf, Zr, and Si of 0.5-1.5 weight percent.
 12. The article of claim 1wherein: the coating has 3.0-5.8 said weight percent Ta; and the coatinghas combined contents, if any, of no more than 6.5% by weight Ru, saidTa, and said Re.
 13. The article of claim 1 wherein: the coating hasless than 0.50 weight percent Ru, if any.
 14. The article of claim 1wherein: the coating has less than 0.50 said weight percent Re, if any.15. The article of claim 1 wherein: a ratio of said substrate weightpercent Re to said coating weight percent Re, if any, is in excess of10.0.
 16. The article of claim 1 wherein: a SRZ, if any, is less than0.001 inch (0.025 mm) thick.
 17. The article of claim 1 being a turbineblade.
 18. The article of claim 1 wherein at least one of: the substrateis a single crystal alloy; the substrate has a density of 0.315-0.327pounds per cubic inch (8.72-9.05 g/cm³); and the substrate has a creepresistance of at least 50 F (28 C) greater than that of PWA1484.
 19. Anarticle comprising: a Ni-based superalloy substrate comprising, byweight percent: 2.0-3.0 Cr; 2.0-4.0 Mo; 8.0-10.0 W; 2.0-3.0 Ta; 6.0-7.0Al; 6.0-8.0 Co; 4.0-5.0 Re; 6.0-8.0 Ru; and a coating comprising,exclusive of Pt group elements, by weight percent: Ni as a largestcontent 5-11 Al; 3-15 Cr; 9-17 Co; up to 7 Ta, if any; up to 6 W, ifany; up to 3 Mo, if any; 0.05-0.7 Hf; 0.1-0.5 Si; up to 0.7 Y, if any;up to 0.7 Zr, if any; up to 0 Re, if any
 20. An article comprising: aNi-based superalloy substrate comprising, by weight percent: 2.0-3.0 Cr;2.0-3.0 Mo; 7.0-9.0 W; 2.0-4.0 Ta; 5.0-6.0 Al; 7.0-9.0 Co; 3.0-5.0 Re;4.0-6.0 Ru; and a coating comprising, exclusive of Pt group elements, byweight percent: Ni as a largest content 5-11 Al; 3-15 Cr; 9-17 Co; up to7 Ta, if any; up to 6 W, if any; up to 3 Mo, if any; 0.05-0.7 Hf;0.1-0.5 Si; up to 0.7 Y, if any; up to 0.7 Zr, if any; up to 0 Re, ifany